This invention relates generally to systems for formattting digital information, and more particularly, to methods and apparatus for transforming digital information into a format similar to that of a standard color video signal, for subsequent processing by conventional video circuitry.
Systems of this general type are of particular use in recording digital information on a record medium such as a video disc. One such system is described in a copending and commonly-assigned application for U.S. Patent, Ser. No. 66,620, filed Aug. 15, 1979 in the name of W. R. Dakin and entitled "Video Recording Medium for Sto-Motion Playback". In the disclosed system, discrete segments of an analog audio signal are digitized and compressed in time, and recorded as baseband signals on alternate tracks of a video disc. Corresponding frames of a conventional video signal are recorded as fequency-modulated carrier signals on the tracks interleaved with the audio tracks. During playback of the disc, a selected audio track is scanned initially, to recover the recorded digital audio data, and the recovered data is entered into a memory. The track recording the corresponding video frame is then scanned in a repeated fashion, to produce a stop-motion display of the frame, while the stored audio data is extracted from the memory and converted back to an analog format, for simultaneous playback at its original speed.
In the aforedescribed system, the audio information is recorded as a baseband digital signal, whereas the video signal is recorded as a frequency-modulated carrier. Although this signal formattting technique is effective in processing both video and audio information, it has not proven entirely satisfactory, primarily because the frequency spectra of the respective video and audio signals are substantially different and because the audio signal sometimes cannot be transmitted over a standard color video channel.
It thus will be apparent that a need has existed for a digital formatting technique in which digital information is converted into a format similar to that of a conventional color video signal. Also, it will be apparent that a need has existed for a digital formatting technique that takes better advantage of a relatively high signal-to-noise ratio channel such as a recording medium, to record more information in a prescribed bandwidth. The present invention fulfills these needs.